Because of its high caloric density, intravenous fat emulsions have been suggested as useful sources of calories and essential fatty acids in patients with serious heart disease in whom fluid restriction must be closely monitored. Previous studies in the experimental animal have suggested a myocardial depressant effect of intravenous fat emulsions at high infusion rates. In the present study, 19 adult patients, following uncomplicated isolated coronary artery bypass surgery, were divided into two groups. A constant infusion of 2 ml/min of soy oil emulsion (20% Intralipid) was administered to the first group. The second group received 20% Intralipid at 1 ml/min followed by a 2 ml/min infusion. In the group receiving the 2 ml/min infusion (averaging 5.25 mg/kg/min), significant decreases in cardiac output and increases in pulmonary capillary wedge pressure occurred. One patient suffered an adverse side effect which may have been related to myocardial ischemia. The second group of patients received an initial infusion of 1 ml/min (averaging 2.35 mg/kg/min) following which the rate was doubled. No significant hemodynamic changes or adverse side effects occurred in the second group. It is concluded that 20% soy oil emulsion can be administered safely to the recently postoperative cardiac surgical patient recovering from coronary bypass grafting, but the rate should not exceed the maximum clearance rate of 1 ml/min (2.67 mg/kg/min).